Kevin Costner risking millions for 'Horizon' isn't lost on his co-stars: 'You're driven to work very, very hard to support this dream of his'

"You just want to do well for this man, because he's given his heart and soul to making it," Sienna Miller says of Costner.

A photo illustration of 'Horizon' stars Sienna Miller, Kevin Costner and Luke Wilson.
Sienna Miller, Kevin Costner and Luke Wilson talk to Yahoo Entertainment about making Horizon. (Photo illustration: Yahoo News; photos: Steve Granitz/FilmMagic via Getty Images)

Kevin Costner invested his blood, sweat, tears — and $38 million of his own money — into Horizon: An American Saga. The four-part western epic is Costner's passion project, and what he's risked to bring the first film to life is not lost on his co-stars.

"It didn't add extra pressure," actor Luke Wilson told Yahoo Entertainment, "but I certainly did take it into account. When he hired me, he did tell me that he was putting his own money into it. He told me that he had this piece of land in Santa Barbara and he was putting that on the line, which to me, I just think that's unbelievably cool."

Costner, who funded the movie alongside two mystery investors, has openly discussed how he mortgaged his sprawling 10-acre beachfront home in Montecito, Calif., that's worth more than $100 million. The Oscar-winning actor, who also directed and wrote the saga, previously told Yahoo that while he "never thought" he'd acquire such nice things, money can't "keep me from my dream. I can't be a slave to this other stuff I have."

Wilson said he's moved by Costner's passion.

"In hearing him these past few weeks talk about it, he talks about people just trying to make their pile of money in life bigger and bigger, and he says he just wants to push it all in on telling a story that he cares about," the Old School star explained. "It all comes from the top, and all we all wanted to do was just to do a good job [for] him because there's so much going on. When he hired each one of us, he said, 'And I'll need your help too.' That's something I've never heard from a director, that I'll need your help."

Sienna Miller, who plays settler Frances Kittredge in the film, told Yahoo that everyone on set was motivated to support Costner's "dream."

"I think you're really driven to work very, very hard to support this dream of his and how much he's personally invested in it," she explained. "There were no executives on set, there wasn't the presence of a studio. It felt like a very big-budget independent film. You just want to do well for this man, because he's given his heart and soul to making it."

The British actress said it was a no-brainer to join this project. "I grew up in the '90s, so Kevin Costner was everything to me in my childhood," she explained. "There was no way I was not going on this journey."

Actor Sam Worthington said he didn't feel added pressure knowing what Costner had invested, but said the Yellowstone star's willingness to take risks made him want to hop onboard.

"I love working with a director that takes big risks, and this certainly was that," the Avatar star explained, adding, "Any movie is taking risks, you never know what's going to connect with an audience."

Costner told Yahoo, "Clearly things are at risk" with these films. However, he doesn't "want to lose track of what moves me and what I want to do in my life."

Warner Bros. is releasing the first two films this summer. Horizon: An American Saga – Chapter 1 hits theaters June 28, and Chapter 2 follows later on Aug. 16. Chapters 3 and 4 have not been shot and are not entirely funded yet.

Costner revealed that, for him, Horizon will be considered a success if people "want to see it again" and "share it" with loved ones. "Sharing is a sign of something that moves you," he said.

Horizon: An American Saga Chapter 1 is in theaters on June 28.